A sentry is someone who stands guard or watches against some intrusion or unwelcome activity. Your dog stands sentry over your house, but he would be more effective if he barked at strangers instead of licking their hands.

The noun sentry came from the French sentinelle, which has a similar meaning. It was in the 17th century that the word was first associated with someone on a watchtower as a military guard. You could only enter the dreaded ice fortress after sneaking past the sentry posted outside. Don't let his button eyes and carrot nose fool you — he's a sharp one!

Definitions of sentry
  1. noun
    a person employed to keep watch for some anticipated event
    synonyms: lookout, lookout man, picket, scout, sentinel, spotter, watch
    see moresee less
    type of:
    security guard, watcher, watchman
    a guard who keeps watch
Word Family

Test prep from the experts

Boost your test score with programs developed by’s experts.

  • Proven methods: Learn faster, remember longer with our scientific approach.
  • Personalized plan: We customize your experience to maximize your learning.
  • Strategic studying: Focus on the words that are most crucial for success.


  • Number of words: 500+
  • Duration: 8 weeks or less
  • Time: 1 hour / week


  • Number of words: 500+
  • Duration: 10 weeks or less
  • Time: 1 hour / week


  • Number of words: 700+
  • Duration: 10 weeks
  • Time: 1 hour / week